what would happen if a pre-veil entity and a post-veil entity interacted?

[anagogy]

Just as an aside and to further the discussion, before the veil, there was no STS. According to Ra, creation of the veil = creation of STS = creation of free will. The veil gives us the free will to choose to not recognize the unity in all of creation. Before the veil, we weren't afforded that exquisite "opportunity". If you recognize the unity of Creation, there is no way to serve the self without serving the all from the get go. The veil sets up for us the illusion of a choice between the two.

To continue that train of thought: I think it is also worth mentioning for the sake of its interesting nature, that an unveiled being is still not omniscient, and thus, while they would most certainly default to recognizing the unity of creation just as you say, they still might "make mistakes" that resulted in disharmony to others. However, they would be innocent accidents rather than deliberate excursions into negativity.